CVE-2021-47013

In the Linux kernel, the following vulnerability has been resolved:

net:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send

In emac_mac_tx_buf_send, it calls emac_tx_fill_tpd(..,skb,..). If some error happens in emac_tx_fill_tpd(), the skb will be freed via dev_kfree_skb(skb) in error branch of emac_tx_fill_tpd(). But the freed skb is still used via skb->len by netdev_sent_queue(,skb->len).

As i observed that emac_tx_fill_tpd() havent modified the value of skb->len, thus my patch assigns skb->len to len before the possible free and use len instead of skb->len later.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/16d8c44be52e3650917736d45f5904384a9da834
• https://git.kernel.org/stable/c/55fcdd1258faaecca74b91b88cc0921f9edd775d
• https://git.kernel.org/stable/c/6d72e7c767acbbdd44ebc7d89c6690b405b32b57
• https://git.kernel.org/stable/c/8c06f34785068b87e2b560534c77c163d6c6dca7
• https://git.kernel.org/stable/c/9dc373f74097edd0e35f3393d6248eda8d1ba99d
• https://git.kernel.org/stable/c/c7f75d11fe72913d2619f97b2334b083cd7bb955
• https://git.kernel.org/stable/c/dc1b438a35773d030be0ee80d9c635c3e558a322
• https://git.kernel.org/stable/c/e407495ba6788a67d1bd41714158c079e340879b
• https://git.kernel.org/stable/c/16d8c44be52e3650917736d45f5904384a9da834
• https://git.kernel.org/stable/c/55fcdd1258faaecca74b91b88cc0921f9edd775d
• https://git.kernel.org/stable/c/6d72e7c767acbbdd44ebc7d89c6690b405b32b57
• https://git.kernel.org/stable/c/8c06f34785068b87e2b560534c77c163d6c6dca7
• https://git.kernel.org/stable/c/9dc373f74097edd0e35f3393d6248eda8d1ba99d
• https://git.kernel.org/stable/c/c7f75d11fe72913d2619f97b2334b083cd7bb955
• https://git.kernel.org/stable/c/dc1b438a35773d030be0ee80d9c635c3e558a322
• https://git.kernel.org/stable/c/e407495ba6788a67d1bd41714158c079e340879b